1. Field of the Invention
The invention relates to a heart replacement system for use in experimental animals and, ultimately, in the human body. More specifically, the invention relates to such a system which includes a pump means and elements for driving the pump means, the elements being attached to skeletal muscles and being actuable by sequential stimulated contraction of skeletal muscles.
2. Description of the Prior Art
The search for an implantable heart replacement system to replace a diseased heart no longer capable of sustaining life despite optimal medical or surgical intervention has identified the following requirements--an implantable power source for a blood pump; an implantable blood pump capable of reproducing the pump functions of the natural heart; and a control system for altering the performance of the blood pump in response to body needs.
Approaches to an implantable power source have included nuclear isotopes providing thermal power and batteries storing electrical power. (Ref.--Artificial Heart Driving Systems--Historical Review and Future Possibilities, Mrava GL, Adv. Biomed. Eng. Med. Phys. 3:31-68, 1970; Power Systems for Artificial Hearts, pp. 922-36, Mohnhaupt. R. et al, in Hwang NH, Normann NA, ed. Cardiovascular Flow Dynamics and Measurements, Baltimore, Univ. Park Press 1977 WG 106 N 111c 1975; U.S. Pat. No. 4,058,857, 1977, Runge et al; and U.S. Pat. No. 4,221,548, 1980, Child.) The nuclear power approach has been limited by problems of heat dissipation and radiation poisoning. The electric battery approach has been limited by the need for frequent recharging.
Skeletal muscle has been used in various methods to augment the performance of the natural, diseased heart. (Ref.--Macoviak J.A., Surgical Forum 1980, pp. 270-271, vol. XXXI; Drinkwater, D.C., Surgical Forum 1980, pp. 271-274, vol. XXXI). The methods described involve repositioning of skeletal muscle from its original anatomic location to a position on the wall of the natural heart or a vessel arising from the heart. These methods are limited by the fibrosing tissue response to repositioning of the muscle which compromises the contractile performance of the repositioned muscle, by the difficulty in protecting the blood supply of the repositioned muscle, and by the physiologic differences between skeletal muscle and heart muscle, skeletal muscle being more fatiguable than a comparable amount of heart muscle.
Multichannel skeletal muscle stimulators have been developed for artificial electrical stimulation of skeletal muscles in the limbs of paraplegic patients to restore the ability to walk, and in the backs of children with scoliosis to effect a correction of the skeletal deformity. (Ref.--Stroznik, P., IEEE Transections on Biomedical Engineering, vol. BME--26, No. 2, Feb. 1979, pp. 112-116; Hralj, A., Med. Progress Technol., 7, 1980, pp. 3-9; Axelgaard, J., Orthop. Trans. 4, 29-30, 1980.) In these methods, artificial activation of the skeletal muscles causes a locomotory or postural effect similar to that resulting from natural activation of the muscles.
Approaches to an implantable blood pump capable of reproducing the pump functions of the natural heart are varied. One approach has been to incorporate a large passive chamber, simulating the natural atrium, between each active ventricle chamber and the vein from which blood is drawn into the ventricle chamber during diastole. This approach is intended to reduce the deleterious suction effect causing collapse of the vein during diastole and thereby limiting filling of the ventricle. (Ref.--Nose Y., Trans. Amer. Soc. Artif. Int. Organs. 1966, vol. XII, pp. 301-311). This approach is limited by sludging of blood in the large atrial chamber, predisposing the blood to clotting.
Other approaches have been directed to minimizing destruction of blood elements by using a pneumatically activated polyurethane membrane to pressurize blood in the artificial ventricle. (Ref.--Hessler, T. R., Trans. Am. Soc. Artif. Intern. Organs. vol. XXIV, 1978, pp. 532-536). While polyurethane does have suitable blood contacting properties, the noncorrugated design of the membrane necessitates a large diameter membrane in order to effect a suitable blood stroke volume. Blood pumps with such a large diameter membrane have been limited by blood stagnation at the periphery of the membrane.
Other approaches in blood pump design provide inherent control of blood stroke volume by venous filling pressure. (Ref.--Kwan-Gett, C. S., Trans. Am. Soc. Artif. Int. Organs., 1969, vol. XV, pp. 245-266; Pierce, W. S., Surgery, Aug. 1981, pp. 137-147). In these designs, each half of the blood pump acts independently of the other half in its response to changes in venous filling pressure.
Various control systems have been described for altering the cycling rate of an implantable blood pump in response to changing perfusion requirements of the body. Some systems rely on measurement of left atrial pressure and aortic pressure by fluid filled catheters connected to remote transducers. Other systems are described which relate to blood pumps powered pneumatically by an external air pump. These systems rely on deriving left atrial and aortic pressures from analysis of the air pressure wave driving the blood pump. (Ref.--Landis, D. L., Trans. Am. Soc. Artif. Intern. Organs., 1977, vol. XXIII, pp. 519-525; and U.S. Pat. No. 4,086,653, 1978, Gernes).